IGBT vs. MOSFET : An Up-Close Look
Example Application Analysis
Disclaimer: This is a loss estimation analysis. The results and conclusions
are based on simplified assumptions, and are not intended to replace
additional rigorous analysis and testing that is also required, but rather to
supplement such efforts.
Renesas Electronics America Inc.
Satya Laud, Product Marketing
Jan 30, 2014
Rev. 1.00
© 2012 Renesas Electronics America Inc. All rights reserved.
00000-A
Example Application Considerations
Defining the Design Requirements
Motor Inverter Application Details
Parameter/Specification
Value
Motor Type
3 ph,
PMSM
Units
Comments
Rated Power
1.5 kW
kW/hp
1 hp = 0.75 kW
Rated rms current
4.9
Arms
Irms = Pout / (1.732 x Vrms x 0.9 x 0.9)
Rated rms voltage
220
Vrms
PWM switching frequency
20
kHz
Maximum DC bus voltage
400
Vdc
Maximum Ambient Temperature
45
deg C
Maximum Heat Sink*/PCB Copper Temperature
90
deg C
*In case devices are heat sinked
Package preference for the IGBT/FET
TO-247
Gate Driver sourcing/sinking current rating
1
A
TO-3P is also acceptable
This is usually specified on the gate driver's
datasheet
Maximum or Blocked Rotor current Limit
9.7
Arms
2 x Rated RMS Current
Maximum or Blocked Rotor current duration
1
s
Any Special Requirements, Considerations
Yes
PMSM = Permanent Magnet Synchronous Motor
1. Short Circuit Ruggedness > 5 us is desired
2. Sine Wave PWM switching algorithm is used
User Inputs
Qualitative Review of the Requirements:
 Power level is 1500 W => Likely Better suited to IGBT + FRD
 Fsw is 20kHz => MOSFET or IGBT + FRD could be used
 DC bus voltage is 400V (maximum) => 500 V or higher rated IGBT + FRD
or MOSFET would be required
 Diode recovery loss important => IGBT + FRD or Fast Body Diode type
MOSFET would be essential
 At least 5 us SC withstand capability is needed => IGBT + FRD has to be
selected accordingly; most HV MOSFETs have more than this capability
 Lowest Possible Device Cost is Important => IGBT+FRD would be better
An IGBT+FRD would likely be a better choice..!
First Pass selection of a candidate MOSFET
Basic Requirements:
• BVdss >= 500 V
• Id @ Tc = 25 C >= 2 x blocked rotor current
Key Features
and
Specifications
of Relevance
So we pick the
RJL5020DPK as
the first pass
candidate..!
First Pass selection of a candidate IGBT + FRD
Basic Requirements:
• BVdss >= 500 V
• Ic @ Tc = 25 C >= 2 x blocked rotor current
Key Features
and
Specifications
of Relevance
So we pick the
RJH60M5DPQ as
the first pass
candidate..!
Loss Considerations and Assumptions
Conduction Loss Calculation Procedure and Assumptions:
1. The RMS value of the current is used with 100 C value of Rdson
for conduction loss estimation in MOSFET
2. The RMS value of the current is used with 100 C value of
Rce(on), which is (Vce(sat)/Ic,sat at 100 C).
3. A 1 V drop is assumed to account for the minimum forward drop
across the IGBT, this is included in the conduction loss
calculations
4. The conduction time durations are assumed 50% for the
MOSFET and body diode and IGBT and FRD (this is a
simplification since the actual conduction times will vary along
the line cycle)
Note: The assumptions lead to approximations in the estimated
values of loss and operating junction temperature, so it is best
to bench test devices under actual application conditions..
Loss Considerations
Switching Loss Calculation Procedure and Assumptions:
1. The MOSFET rise and fall times are estimated based on 1 A
gate driver current and the total Qg from the datasheet
2. The Qrr (reverse recovery charge) is estimated as 0.5* Irrm * trr,
where Irrm is set equal to 1/3 rated IF since the selected
MOSFET datasheet did not specify this value
3. The average value of the current is used to estimate switching
loss (the instantaneous value varies along the sine wave cycle)
4. The diode recovery loss is included in the switching loss for the
IGBT and for the MOSFET
5. The Eon and Eoff values on the IGBT datasheet are scaled for
voltage, current, and temperature
Note: The assumptions lead to approximations in the estimated
values of loss and operating junction temperature, so it is best
to bench test devices under actual application conditions..
Loss Considerations and Assumptions
IGBT Simplified Loss Equations:
Ploss_IGBT = Pcond_igbt + Psw_igbt
= {(Vce_zero x Ic_avg) + (Ic_rms2 x Rce_on_hot)} + [(Eon_hot_scaled + Eoff_hot_scaled) x Fsw]
Where:
Ploss_IGBT = total loss in the IGBT
Pcond_igbt = conduction loss in IGBT
Psw_igbt = switching loss in IGBT
Vce_zero = initial ‘knee’ voltage of IGBT (~ 1 V for 600 V rated IGBTs)
Ic_avg = average value of the current flowing in the IGBT assuming a sinusoidal waveform
Ic_rms = RMS value of the current flowing in the IGBT assuming a sinusoidal waveform
Rce_on_hot = equivalent ‘on-resistance’ of the IGBT at elevated junction temperature
Eon_hot_scaled = turn-on loss of the IGBT scaled for the voltage and current being switched
Eoff_hot_scaled = turn-off loss of the IGBT scaled for the voltage and current being switched
Fsw = switching frequency
Note: The assumptions lead to approximations in the estimated
values of loss and operating junction temperature, so it is best
to bench test devices under actual application conditions..
Loss Considerations and Assumptions
MOSFET Loss Equations:
Ploss_fet = Pcond_fet + Psw_fet
= {Id_rms2 x Rds_on_hot} + [(Vbus x Ids_avg x (trise + tfall) x 0.5) + (Prr x Fsw)]
Where:
Ploss_FET = total loss in the MOSFET
Pcond_fet = conduction loss in the MOSFET
Psw_fet = switching loss in the MOSFET
Id_rms = RMS value of the current flowing in the MOSFET assuming a sinusoidal waveform
Rds_on_hot = on-resistance of the MOSFET at elevated junction temperature
Vbus = DC bus (link) voltage
Ids_avg = average value of the current flowing in the MOSFET assuming a sinusoidal waveform
Trise = rise time (turn-on time)
Tfall = fall time (turn-off time)
Prr = loss component due to reverse recovery of the body diode
Note: The assumptions lead to approximations in the estimated
values of loss and operating junction temperature, so it is best
to bench test devices under actual application conditions..
Estimated Device Loss and Tj Summary:
RJH60M5DPQ (IGBT+FRD)
Pout(W)
1500
1500
Fsw
(kHz)
20
5
Loss (W)
16.6
9.7
Tj (deg C)
100.4
96.1
RJL5020DPK (MOSFET)
Pout (W)
1500
1500
Fsw (kHz) Loss (W)
22
20
5
8.7
Tj (deg C)
103.7
95.4
Summary:
- The IGBT has the advantage at higher frequency due to better
switching loss performance (lower diode recovery loss)
- The MOSFET has the advantage at lower frequencies (below say 8
kHz) due to lower conduction loss (a MOSFET has no ‘knee’ in its
forward characteristics as does an IGBT)
Conclusions:
 IGBTs and HV MOSFETs are similar in many ways, but differ
from a performance and application perspective
 The analysis done here has assumptions, but it indicates
that MOSFETs even with the faster recovery body diode
suffer a much higher switching loss compared to the
IGBT+FRD
 In case the switching frequency is lowered then the
MOSFET wins over the IGBT, primarily due to the
significantly reduced impact of the diode recovery loss
 It is best to test sample devices on a bench before making
any final selections
Renesas Electronics America Inc.
© 2012 Renesas Electronics America Inc. All rights reserved.